Process for lowering the swelling in water of viscose cellulose by cyanoethylation in the presence of specific alkali metal salts



United States Patent Pieter Paulusma, Arnhem, Netherlands, assignor toAmerican Enira Corporation, Erika, N.C., a corporation of Delaware NoDrawing. Filed Diet. 3, 1962, 'Ser. No. 228,025 Claims priority,application Netheriands, Oct. 9, 1961,

9 Claims. 0!. 8-1162) .This invention relates generally to theproduction of I improved regenerated cellulose products and moreparticularly to a process for lowering the degree of swelling ofregenerated cellulose products in water, especially viscose rayon fibersand fabrics.

It is known that the degree of swelling of regenerated celluloseproducts in water can be changed by successively treating them with anaqueous solution of an alkali metal hydroxide and acrylonitrile.However, by this process the degree of swelling of, for example, rayonstaple fibers, is substantially increased. While such a relatively highdegree of swelling may be favorable when the staple fibers are used inguaze bandages or analogous products, it is generally not desirable.Under most circumstances staple fibers or threads of regeneratedcellulose should have a relatively low swelling value, particularly ifthey are processed into woven or knitted fabrics. This is because thedimensions of woven and knit-ted fabrics of regenerated cellulose yarnsare, as is known, less stable than fabrics made of cotton fibers, whichhave a lower degree of swelling in water than do staple fibers orthreads of regenerated cellulose.

. It is therefore an object of this invention to provide regeneratedcellulose products that have a low degree of swelling in water.

Another object of this invention is to provide a process for treatingregenerated cellulose products to lower their degree of swelling inwater.

Still another object of this invention, is to provide a process forproducing regenerated cellulose products that absorb less moisture fromthe atmosphere. I

These and other objects will become apparent from the following detaileddisclosure In accordance with applicants invention, regeneratedcellulose products are first treated with an acqueous hydroxide solutionthat has a normality not higher than 0.70 and containsat least one saltof an alkali metal hydroxide and an inorganic acid derived from one ofthe first five anions of the lyotropic series according to Hofmeister(see E. A. Hauser, Collodial Phenomena, page 132, First Edition, 1939).Thereafter, the pro-ducts are treated with an azeotropic mixture ofacrylonitrile and where A is the weight of the air dried cellulosepro-duct and B is the weight of the product after it had been soaked inwater for two hours and centrifuged for ten minutes.

Surprisingly, if the normality of the hydroxide solution is higher than0.70, the treated products have a cce higher degree of swelling than dothe untreated products. Thus, in order to obtain low swelling products,the normality of the hydroxide solution must be below 0.70. Moreover,applicant has discovered that the decrease in degree of swelling oftreated products increases as the normality of the caustic solutiondecreases.

The alkaline metal hydroxides that may be'used in the process includelithium hydroxide, sodium hydroxide, potassium hydroxide, rubidiumhydroxide, and cesium hydroxide. However, for economy reasons, it ispreferred to use sodium hydroxide. The salts added to the causticsolution may be lithium salt, sodium salt, potassium salt, rubidiumsalt, or cesium salt, although, also for economy reasons, it ispreferred to use sodium salts. The :salts are derived from an alkalimetal hydroxide and any one of the following acids: sulfuric acid,hydrofluoric acid, nitric acid, hydrochloric acid, and hydrobr-omicacid. The anions of these acids are the first five members of thelyotropic series according to H-ofmeister. Preferably, sodium sulphateor sodium chloride is added to the caustic solution since these saltsare commercially available at a low price.

It has been found that the reaction may be accelerated by increasing theamount of salt in the caustic solution, the amount of salt added beingdependent on the desired decrease in the degree of swelling in theproduct treated. The temperature at which the treatment with thehydroxide solution is carried out may vary between wide limits. However,higher temperatures are desirable since the wet strength of the productdecreases to a lesser extent. Also, the time during which the productsare treated with the hydroxide solution preferably should be as short aspossible to limit the decrease in the wet strength of the product. Ifneeded, a wetting agent may be added to the hydroxide solution.

After the products have been treated with the hydroxide solution, excessliquid may be removed by centrifuging or pressing. The products are thentreated witha mixture of acrylonitrile and a small amount of water. Thetemperature of the acrylonitrile mixture i maintained as high aspossible in order that the/treatment may be short, thus allowing theprocess to be carried out in a continuous manner. For example, thetreatment may be carried out at 70 C. using an azeotropic mixtureconsisiting of 88% of acrylonitrile and 12% water. If the treatment iscarried out under pressure, even higher temperatures may be used.Alternatively, a mixture of acrylonitrile and a diluent, such asbenzene, toluene, acetone, or chloroform may be used. The amount ofacrylonitrile reacting with the products may vary within wide limitsdepending on the decrease in the degree of swelling desired.

Products treated in accordance with this invention not only have a lowerdegree of swelling in water, but also absorb less moisture in air. As aresult of the treatment, the percentage of moisture absorbed from airmay be reduced to below 8%. which corresponds to a moisture absorptionof about 1 2% for untreated products of regenerated celiulose in air at20 C. and a relative humidity of 65%.

'The invention will .be more clearly understood from the followingexamples. However, these examples are not to be construed as limitative.Percentages are given by weight unless otherwise indicated.

EXAMPLE I Viscose rayon staple fibers having a denier of 1 /2 wereseparated into several samples and each sample treated with an aqueoussodium hydroxide and salt solution.

ment lasted one minute. After the treatment each sample was centrifugedand weighed. Thereaftenthe samples were treated with acrylonitrilecontaining 2% water at 20 C. With the exception of run 4, the durationof the treatments was such'that equal percentages of acry- EXAMPLE 11Samples of staple fibers from thesame batch as those .lonltrrle werebound to all samples. vThe reaction be- Example I Were treated sodlllmhydfoxlde and tween the regenerated cellulose and acrylonitrile to pro-Salt $0111t1011 In a mannfif analogous that Of EXample duce acyanoethylated product may be expressed by the In runs I0 however, thesodlum Sulphate 0011- f ll i ti tent was varied. The fibers pre-treatedwith the sodium 7 81k 10 hydroxide .solution were then treated with anazeotropic regen. cellulose0H GH =CHCN mixture of 88% by weightacrylonitrile and 12% by regen.cellulose0CHzCHzCN weight water at about70 C. In runs 16 to 21 salts The percentage acrylonitnile bound to theregenerated other 'E sodlllm Sulfate were added to h Sodium "celluloseis calculated-by determining the amount of nitrohydrQxlde 5Q11l11011- InI 22 the temperature of thc genin the dry final product according to thewell-known caustic solution was C. The results are set forth 1n Kjeldahlmethod. From the amount of nitrogen present Table p I in the finalproduct, the numberof cyanoethyl groups may Run3 11 to 15 Show that ymcfreaslng the Sodlllm $111 be determined and such determinationexpressed as the P Content the reactlonls' conslderablyaccelelatfidweight percent of acryloni-trile bound to the final product.Runs 15 to 19 Show the afflicts Obtained using Sodium After thetreatment with acrylonit-rile, the samples were 20 chlfmde, PotasslumSulfate, Sodium nitrate, and Sodium successively washed with diluteacetic acid and warm wafluoflde as the Salts added 0 h Caustic Soluti n.AS ter and then dried. shown in runs 20 and 21, salts which are notderived from The degree of wellin was determin d f th the first fiveanions of thelyotropic series not now effect a formula: decrease in thedegree of swelling of the fibers. In run 22 A 25 the disadvantage ofusing a low hydroxide solution tem- X 100% perature is shown. Thus, theuse of a low temperature in the treatment yields fibers of considerablylower strength where A is the weight of the air dried fibers and B isthe than does the use of a high temperature. weight of the fibersimmediately following soaking in wa- I A ter for two hours andcentrifuging for 1() minutes. EX MPLE V The conditions and results ofruns 1 to 10 are et A fabric having a warp conslsting of 120 denierconforth in Table I. tinuous filament viscose rayon threads and a weftconsist- Table I Hydrox- Percent Tempera- Acryloni- Percent MoistureNormal- Percent Temp. ids soluincrease ture acrytrile treatacryloni-Deg. 0i Wet absorp- Hydroxityofhy- Salt saltinhyhydroxtiontreatin Weightlonitrile/ ment in trile swelling strgh., tion in ide droxide droxideide solument after cen- H2O, time bound to inwater gJd. air at solutionsolution tion, C. time trifuging .G. (minutes) fibers 20 (3.,

. (minutes) 5 RH. 65%

Control 1 NaOH- 0.10 Nagsol- 5 90 1 20 720 19 11.7 0. 20 M12801 5 90 120 240 19 7. s 0. 50 Na SO4 5 90 1 20 150 19 7. 7 0. 50 Na SO 5 90 1 6320 240 35 6. 1 0. Na2s04 5 1 73 20 19 7. 7 0.80 Nafls 4- 5 90 1 s0 20 9019 7.8 1.0 Naflso4 5 90- 1 s9 20' 5 80 19 7.9 1. 6 Nagsol 5 90 1 20 4019 7. 6 2. 5 Na-2S04 5 90 1 241 20 15 19 7.8 0. 5 Nflasol 5 90 1 42 30300 19 Table 11 Hydrox- Percent Acrylo- Percent Normal- Percent.Hydroxide solu increase Temperanitrile acrylo 7 Deg. of Wet Hydroxity ofSalt salt in ide solution in weight ture acrytreat ient nitrile swellingstrength, ide hydroxide hydroxide tion treatment after cenlonitrile/time bound to in water g./d.

solution solution temp, O. time triiuging water, O. (minutes) fibers(minutes) ControL. '11 NaOH. 0.1 Na2sO4 1 90 1 40 70 5 6.7 NaOH 0.1NazSOl--- 5 90 1 39 70 5 15. 9 NaOH--- 0.1 N8zSO4-.. 10 90 1 41 70 5 17.2 NaOH 0. 1 Na2SO4 15 90 1 43 70 5 1s. 7 NaOH... 0.1 NSZSOA- 20 90 1 4470 5 19.1 NaOH 0.1 NaCl- 5 90 1 44 70 5 12.2 Na-OHW 0.1 K1S01 5 90 7 145 70 5 13.4 NaOH 0.1 NaNO 5 90 .1 41 70 5 16.6 NaOH 0.1 NaF 5 90 1 3870 5 20.6 NaOH--- 0. 2 KI 46 90 1 96 70 2% 23.1 NaOH.-- 0.1 Na2HPO4. 2590 1 44 70 5 0.4 NaOH 0.1 NazSOr--- 5 20 1 44 70 5 16.5

The table shows that using a sodiurnhydroxide solution having anormality of 0.7 or lower results in a decrease of swelling. Theuntreatedcontrol fibers had a degree of swelling of 75. Fibers treatedaccording to runs 1 to 5 had a degree of swelling of 55, 58, 60,44and7l,

.ing of a yarn made of-1 /2 denier viscoserayon staple fibers, waspassedthrough an aqueous bathmaintained at 90 C. containing 1% by weightsodium hydroxide and 5% by weight sodiunrsulfate, The residence time'ofthe 75 fabric in the bath was one minute. Excess liquid was removed fromthe fabric by means of pressure rollers. The fabric was then passedthrough a bath maintained at about 7 C., containing 88% by weightacrylonitrile and 12% by weight water. The residence time of the fabricin this bath was 2 minutes. Excess liquid was removed from the fabric bymeans of pressure rollers and the fabric was then successively treatedwith dilute acetic acid and warm water. Thereafter, the fabric wasdried. The weight of the treated fabric was 124.7% of its originalweight. The fabric was immersed in water and afterwards centrifuged. Itthen contained about 63% by weight water. A similar sample of untreatedfabric, after wetting and centrifuging, contained about 97% by weightwater.

EXAMPLE IV A selfsupporting film made from viscose was passed through anaqueous bath maintained at 90 C. containing 1% by weight sodiumhydroxide and 5% by weight sodium sulfate. The residence time of the himin the bath was one minute. The film was passed between two rollersthereby removing excess liquid. Thereafter, the film was passed througha bath maintained at 70 C. containing 88% by weight acrylonitrile and12% by weight water. Residence time in this bath was 1 /2 minutes. Thefilm thus treated was passed between two rollers to remove excess liquidand successively washed with dilute acetic acid and warm water. Afterdrying the film was immersed in water and centrifuged. The increase inweight of the film was only 65% in contrast with untreated film,similarly immersed in water and centrifuged which increased 98% inweight.

Various modifications and changes within the scope of the invention willbe apparent to those skilled in the art. Therefore, the invention isintended to be limited only as set forth in the following claims.

What is claimed is:

1. A process for lowering the degree of swelling in water of a dryviscose regenerated cellulose product comprising the steps of treatingsaid product with an aqueous solution of an alkali metal hydroxidehaving a maximum normality of 0.70 for a suflicient period of time toeffect cyanoethylation of the product upon subsequent treatment withacrylonitrile, said solution having present therein in addition to saidalkali metal hydroxide a small amount of at least one salt of an alkalimetal hydroxide and an acid derived from one of the first five anions ofthe lyotropic series of Hofmeister, treating the alkali impregnatedproduct with acrylonitrile for a sufiicient period of time tocyanoethylate the product and to reduce the degree of swelling of theproduct upon contact with water, and thereafter drying the resultingproduct.

2. A process for treating a dry viscose regenerated cellulose product tolower its degree of swelling in water comprising the steps of immersingsaid product in an aqueous solution of an alkali metal hydroxide havinga maximum normality of 0.70 for a sutlicient period of time to eifectcyanoethylation of the product upon subsequent treatment withacrylonitrile, said solution having present therein in addition to saidalkali metal hydroxide a small amount of at least one salt of an alkalimetal hydroxide and an acid derived from one of the first five anions ofthe lyotropic series of Hofmeister, immersing the alkali impregnatedproduct in acrylonitrile for a sufficient period of time to bind to theproduct from about 6.7% to about acrylonitrile, based on the weight ofthe final cyanoethylated product, and thereafter drying the thustreatedproduct.

3. A process for treating a dry viscose regenerated cellulose product tolower its degree of swelling in water comprising the steps of immersingsaid product for about 70 one minute in an aqueous solution of an alkalimetal hydroxide having a maximum normality of 0.50 and a temperature ofabout 90 (3., said solution having present therein in addition to saidalkali metal hydroxide a small amount of at least one salt of an alkalimetal hydroxide and an acid selected from the group consisting ofsulfuric acid, hydrofluoric acid, nitric acid, hydrochloric acid, andhydrobromic acid, immersing the alkali impregnated product in anazeotropic mixture of acrylonitrile and water for a sufficient period oftime to bind to the product from about 6.7% to about 35% acrylonitrile,based on the weight of the final cyanoethylated product, washing theproduct, and thereafter drying the thus-treated prodnot.

4. A process for treating a dry viscose regenerated cellulose product tolower its degree of swelling in water comprising the steps of immersingsaid product for a maximum of two minutes in an aqueous solution of analkali metal hydroxide having a maximum normality of 0.70, said solutionhaving present therein in addition to said alkali metal hydroxide 5% byweight of said solution of at least one salt of an alkali metalhydroxide and an acid selected from the group consisting of sulfuricacid, hydrofiuoric acid, nitric acid, hydrochloric acid, and hydrobromicacid, immersing the alkali impregnated product in an azeotropic mixtureof acrylonitrile and water main tained at a temperature ranging from 15C.30 C. for a sufiicient period of time to bind to the product fromabout 6.7% to about 35% acrylonitrile, based on the weight of the finalcyanoethylated product, washing the product, and thereafter drying thethus-treated product.

5. A process according to claim 4 in which the alkali metal hydroxide issodium hydroxide and the salt is a sodium salt.

6. The process of claim 5 in which the salt is sodium sulfate.

'7. The process of claim 5 in which the salt is sodium chloride.

8. The process of claim t in which the regenerated cellulose product isviscose rayon staple fiber.

9. A process for treating a dry viscose regenerated cellulose product tolower its degree of swelling in water comprising the steps of immersingsaid product in an aqueous solution of an alkali metal hydroxide havinga maximum normality of 0.70 for a sufficient period of time to increasethe weight of the product by at least 38% after centrifuging, saidsolution having present therein in addition to said alkali metalhydroxide 5% by weight of at least one salt of an alkali metal hydroxideand an acid selected from the group consisting of sulfuric acid,hydrofluoric acid, nitric acid, hydrochloric acid, and h drobromic acid,immersing the alkali impregnated product in an azeotropic mixture ofacrylonitrile and water maintained at a temperature of C. for asufircient period of time to bind to the product from about 6.7% toabout 35% acrylonitrile, based on the weight of the final cyanoethylatedproduct, washing the product, and thereafter drying the thus-treatedproduct.

References Cited by the Examiner UNITED STATES PATENTS 2,332,049 10/43Bock et a1. 2,786,735 3/57 Compton et 211. 2,857,239 10/58 Bikales.3,018,156 1/62 Bikales. 3,101,276 8/63 Hendriks 8--116 XR FOREIGNPATENTS 732,779 6/ 55 Great Britain. 812,063 4/59 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

1. A PROCESS FOR LOWERING THE DEGREE OF SWELLING IN WATER OF A DRYVISCOSE REGENERATED CELLULOSE PRODUCT COMPRISING THE STEPS OF TREATINGSAID PRODUCT WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDEHAVING A MAXIMUM NORMALITY OF 0.70 FOR A SUFFICIENT PERIOD OF TIME TOEFFECT CYANOETHYLATION OF THE PRODUCT UPON SUBSEQUENT TREATMENT WITHACRYLONITRILE, SAID SOLLUTION HAVING PRESENT THEREIN IN ADDITION TO SAIDALKALI METAL HYDROXIDE A SMALL AMOUNT OF AT LEAST ONE SALT OF AN ALKALIMETAL HYDROXIDE AND AN ACID DERIVED FROM ONE OF THE FIRST FIVE ANIONS OFTHE LYOTRIPIC SERIES OF HOFMEISTER, TREATING THE ALKALI IMPREGNATEDPRODUCT WITH ACRYLONITRILE FOR A SUFFICIENT PERIOD OF TIME TOCYANOETHYLATE THE PRODUCT AND TO REDUCE THE DEGREE OF SWELLING OF THEPRODUCT UPON CONTACT WITH WATER, AND THEREAFTER DRYING THE RESULTINGPRODUCT.